Bender type electromechanical device with dielectric operating element



Oct. 18, 1949. H. JAFFE 2,484,950

manna TYPE ELECTROMEGHANICAL DEVICE um! nmwc'rarc ornrwrme ELEMENT FiledApril 9, 1947 2 Sheets-Sheet 1 mwzmm HANS JAWE Oct. 18, 19495 H. JAFFE2,484,950

BENDER TYPE ELECTROMECHANICAL DEVICE WITH DIELECTRIC OPERATING ELEMENTFiled April 9, 1947 2 Sheets-Sheet 2 AC SIGNAL TERMINALS 47 I I FIG. 5

AC SIGNAL TERMINALS 57 FIG. 6

INVENTOR. HANS JAIF'FE A TORNEY 1 Pmnaaoa. 18, 19.49

ENTI OFFICE BENDEB TYPE ELECTROMECHANICAL DE VICE WITH DIELECTRICOPERATING ELE- MENT Hans Jafle, Cleveland Heights, Ohio, assignor to TheBrush Development Company, Cleveland, Ohio, a corporation of OhioApplication April 9, 1947, Serial No. 740,461

. 6 Claims.

This invention relates to electromechanical transducers of the generaltype known as benders, in which mechanical action results from theapplication of an electric held and vice versa. More particularly, itrelates to improved bender type electromechanical devices which arehighly stable with reference to temperature and humidity conditions.

Electromechanical transducers of the piezoelectric type are well knownin the art. One such arrangement has comprised Rochelle salt as theoperating element thereof and transducers of this type are widely usedcommercially. However, the properties of Rochelle salt are such thattransducers comprising this material as an operating element do notprovide entirely satisfactory operation under some operating conditions.For example, the temperature of such a unit must be maintained at alltimes below a rather low maximum value or otherwise the piezoelectricproperties of the operating element are destroyed. Also, it is wellknown that such operating elements are somewhat fragile and, inasmuch asRochelle salt is hygroscopic, it is necessary in trans ducers of thetype under consideration to insure that the operating properties of theunit are not adversely affected by humidity conditions.

Electromechanical transducers of the bender type are also well known inthe art, being described, for example, in U. S. Letters Patent Re'.20,213, granted to C. B. Sawyer on December 22, 1936. Such benderelements, as heretofore used,

have generally comprised an operating element consisting of two layersof some piezoelectric material.

In the research work leading to the present invention, it was discoveredthat certain ceramic materials, having-some very desirable operatingcharacteristics, could be utilized to provide an operating elementgenerally analogous to that of a iezoelectric operating element. Onesuch arrangement is described in full in my copending application,Serial No. 740,460, filed concurrent- 1y with the present invention andassigned to the same assignee as the present invention. This copendingapplication discloses an arrangement using a ceramic dielectric materialwhich is polarized to provide an action somewhat of the nature of thatprovided by the crystal which is frequently used in crystal transducers.The specific arrangement disclosed in the copending application forpolarizing the material of the operating element comprises theapplication of a high unidirectional electrical field thereto. It wouldbe desirable to provide a bender type of operating element for anelectromechanical transducer which uses dielectric material as theoperating element, and it is to this that the present invention isdirected.

It is an object of the present invention to provide an improvedelectromechanical transducer of the type in which mechanical actionresults from the application of an electrostatic field, and vice versa.

It is a, further object of the invention to provide an improvedelectromechanical transducer which may be readily and inexpensivelyproduced and which is rugged and relatively immune to the influences ofextraneous conditions such as temperature and humidity effects.

In accordance with the invention there is provided a bender-typeelectromechanical device comprising an even number of superimposedlayers of dielectric material. These layers comprise two groups ofelements, one of which is to expand while the other group is tocontract, and vice versa, to provide a bender type of electromechanicaltransducer element. There is also provided unidirectional electricalpolarizing means for each of the layers. Also electrical terminalconnections are provided for each of the layers, such that the chargeswhich would be associated with the application of a voltage thereto areof the same sign in each of the layers of one of the two above-mentionedgroups of elements as the charge in each layer of the group due to thepolarizing means, while the charges in each of the layers of the otherof thevtwo above-mentioned groups due to the applied voltage are of theopposite Sign to the charge in each layer of the last-mentioned groupdue to the polarizing means. By this arrangement the device can be usedto convert bending movements'of'the transducer element into electricalenergy, or vice versa.

For a better understanding of the present invention together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

- 3 Referring now to the drawings. Figure 1 is a broken-away isometricview of a phonograph pickup embodying a bender-type electromechanicaldevice in accordance with the invention; Figures 2, 3 and 4 illustratevarious circuit connections suitable for use with the transducer elementof Figure 1; Figures 5 and 6, respectively, illusance with the inventionembodied in a phonograph pickup of well known design. In this phonographpickup, a needle chuck it is mounted on elastic bearings ll, l2 in atwopart molded housing, only one part I! oi which is shown for the sakeof simplicity. Enclosed within the housing is an operating elementcomprising two plates or layers of dielectric material I4, l5 cementedtogether face-to-face, with an electrode l 8 between them and electrodesl1 and I8 on the outer faces. The material of which the elements I4 andI5 are comprised is one which normally does not have the property of asubstantially linear relationship as a first order eifect between itselectrical and mechanical actions but which can be, as described in fullin the above-mentioned copending application, polarized by theapplication of a unidirectional electrical field to respond to thefundamental component of an alternating electrical field applied theretoin at least one mechanical mode. The operating element comprising thelayers l4 and I5 of dielectric material is mounted within the housingbetween similar soft pads i9, 20 of rubber or like material engaging itat one end. The element is engaged at its other end by a fork-likeextension 22 of the needle chuck ID. A thin sheet of rubber or likematerial 23 is disposed between the operating element and the needlechuck to act as a compliant coupling member and to provide insulation toprevent shortclrcuiting of the electrodes l1,- l8 by the needle chuck.The three electrodes are connected to pin-like terminals 25, 26 and 27.

Neglecting for the moment the polarizing action, which is mentionedabove, when lateral vibrations are applied to the needle 28, vibratorybending forces are applied by the chuck to the two-plate crystalassembly, setting up alternating compression and tension forces. Thuswhen the needle is moved in the direction indicated by the arrow A, theplate or layer It is subjected to compression forces and the plate orlayer 15 is subjected to tension forces. Conversely, when the needle isdeflected in direction 13, plate i 5 is subjected to compression forces,and plate i4 is subjected to tension forces. When, as will besubsequently described, the plates are suitably polarized, alternatingpotential difl'erences are developed at the terminals 25, 26, 27 inresponse to the vibrations of the needle. Suitable circuit connectionsfor the arrangements of Figure 1 are illustrated in Figures 2, 3 and 4,in which circuit elements which correspond to those of Figure l haveidentical reference numerals.

Referring now to Figure 2, an arrangement is shown in which theoperating element supplies input signals for a vacuum-tube amplifier 30.Th center electrode iii of the operating element is connected through acondenser 56 to the input electrode of tube 30, theouter electrode i8 ofthe operating element being grounded. The other outer electrode i1 isconnected to a unidirectional source 3| which is used to polarize theoperating elements of the transducer of the invention. The negativeterminal of the source 3| is g ou ded. If the alternating impedance ofthe source Ii is high, a by-pass condenser 32 may be shunted across it.A grid leak resistor 33 is provided for tube 30.

Coming now to a consideration of the operation of the arrangement ofFigure 2,.it will be seen that, with the circuit connection shown, thetwo plates or layers l4 and I5 are connected in series with the battery3i. Under these conditions, the charges resulting from the connection ofthe battery are illustrated by the plus and minus signs to the left ofthe operating element. For alternating currents, however, the two platesare connected in parallel with the input electrodes of tube 30 since theelectrode I1 is effectively connected to the electrode [8 through thepotential source 3! or through the by-pass condenser 12. When the platesare polarized as shown, if a potential were applied to the alternatingcurrent output terminal it would tend to develop charges in one of theplates which correspond in sign to the component of charge developed inthe same plate .by the unidirectional polarizing source ll, whilecharges of reverse sign are simultaneously developed in the other plate.This relationship is illustrated by the plus and minus signs to theright in the operating element. Under these conditions, the inducedcharges due to a bending force are of the same sign as applied to theinput circuit of the vacuum tube 30.

It will be seen, therefore, that the arrangement described comprises aneven number (specifically two) of superimposed layers of dielectricmaterial comprising two groups of elements, one group of which is toexpand while the other group oi which is to contract, and vice versa, toprovide a bender type of electromechanical transducer element. In thecase under consideration there is only one layer (specifically layer I4or- I5) in each of the two groups of elements mentioned.

.Also, it will be seen that the source 3| comprises a unidirectionalelectrical polarizing means for each of the layers mentioned.Furthermore, electrical terminal-circuit connections are provided foreach of the layers such that the charges associated with a theoreticalapplication of voltage thereto, are of the same sign in each of thelayers of one of the two groups of elements as the charge in each suchlayer of the one group due to the polarizing means. Also, it will beseen that the charges in each of the layers of the other of the twogroups of elements due to this theoretical application of voltage are ofopposite sign from the charge in each such layer due to the polarizingmeans. It is therefore seen that the device is used to convert bendingmovements of the transducer element into electrical energy forapplication to the input circuit of tube 30.

In Figure 3 is illustrated an arrangement in which the two plates arepolarized in parallel while being connected in series for alternatingsignals as applied to the input circuit of the tube 30. In Figure 3 theouter electrode I1 is connected directly to the grid of tube 30 whilethe outer electrode i8 is connected to ground. A unidirectional pathbetween the outer electrode I1 and ground is provided by the grid leakresistor 33. The polarizing source 3! is connected between ground andthe inner electrode l6 through a high resistance 35 and a switch 36. Theplus and minus signs shown to the left in the flgure illustrate thecomponents of charge due to the battery action. It will be noted that inthis case the polarity of the upper plate is reversedwith reference tothe polarity shown in Figure 2. However, for signal potentials the upperplate is also reversed as shown by the plus and minus signs to the rightso that the voltages developed by a bending of the element are additivein the input circuit of vacuum tube 30. Here again it will be seen thatthe charges associated with theoretical application of voltage to theplates i'l, l8are of the same sign in the top layer as the charge due tothe action of the polarizing means, while the charge associated with thetheoretical voltage in the bottom layer is of opposite sign from thecharge associated with the battery.

Still another way of utilizing the element of Fig. 1 is illustrated inFig. 4. In this case the outer electrode I1 is connected to the grid ofa tube 38, and the outer electrode I8 is connected to the grid of a tube39. The two tubes have their output circuits connected together througha push-pull transformer 40. Unidirectional paths from the grids andouter electrodes to ground are provided by grid-leak resistors 4|, 42.The two outer electrodes are thus held at the same averageunidirectional potential. The inner electrode I5 is connected throughswitch to the polarizing source 3|. In this case the plates arepolarized in parallel but are effectively in series for signal voltagesas in Fig. 3.

In Fig. 5 there is illustrated a bender element comprising four layersor plates 42, 43, 44 and 45. In order to provide a bender element withfour .3 plates, it is necessary for the plates 42 and to expand when theplates .44 and 45 contract,

p and vice versa. In order to provide this effect so that the unit canbe operated either to convert a bending motion into an electrical outputsignal or an electrical input signal to a bending motion of the element,it is necessary to provide proper circuit connections. The principlewhich is to be followed in this case, also, is that the component ofcharge due to polarizing, of two layers on one 4 side of the centeraxis. should be of the same sign as the component of charge due to thetheoretical application of a voltage to the A. C. terminals of the unitwhile the charges in the other two plates should be of opposite signfrom those due to the theoretical application of voltage. In order toefiect this result, thecircuit connections of Fig. 5 are provided. Thusthe positive terminal of the polarizing source 3| is connected byconductor 41 to the electrode between plates 44 and 45 while thenegative terminal of the source 5| is connected by a conductor 48 to theelectrode between plates 42 and 45. The outside electrodes of plates 42and 45 are connected together by a conductor 49. The alternating-signalterminals 50 and 5| of the unit are illustrated and terminal 50 isdirectly connected to the conductive element between the plates 43 and44 and to the outside electrodes. Terminal 5| is connected to theelectrode between plates 42 and 43 directly and, 66 through an isolatingcondenser 52, to the conductive electrode between plates 44 and 45.

In considering the operation of the arrangement of Figure 5 it will beseen that the components of charge in the plates 42 and 45 due 70 to thepolarizing source 3| are as indicated by the polarity signs to the left.Also, the components of charge due to an applied signal voltage or to aninduced signal voltage in the case of a bending of the element may be asillustrated 7 by the plus and minus signs on the right. Here again it isseen that the components of the two charges under consideration are ofthe same sign in plates 42 and 43 and are of opposite sign in plates 44and 45. As stated above, this is the requirement for bender type ofelement in accordance with the invention. It will be seen. therefore,that the arrangement of Figure 5 comprises an even number (specificallyfour) of superimposed layers of dielectric material comprising twogroups of elements (specifically group 42, 42 and group 44, 45) onegroup of which is to expand while the other group is to contract, andvice versa, to provide a bender type of electromechanical transducerelement. The terminal-circuit connections are such that the chargesassociated with an application of voltage to the A. C. signal terminalsof the transducer elements are of the same sign in each of the layers42, 45 of one of the two groups as the charge in each said layer 42 or43 due to the polarizing means II, while the charges in each of thelayers 44, 45 of the other of the two groups of elements due to thisapplication of voltage are of opposite sign from the charge in each suchlayer 44 or 45 due to the charge therein resulting from the polarizingmeans. This relationship is clearly shown by the polarity signs of thefigure.

A different circuit arrangement is illustrated in Figure 6 where circuitelements which correspond to those of Figure 5 have identical, referencenumerals. In this case, the positive terminal of the polarizing source3| is connected directly to the electrode common to plates 44 and 45 andto, the electrode common to plates 42- and 45 through a resistor 54. Thenegative terminal of source II is connected to the outer electrode ofplate 42, the electrode common to plates 43 and 44, and the outerelectrode of plate 45 through resistors 55, 56 and 51 respectively. Theresistors 54 to 51, inclusive, are isolating resistors for alternatingcurrents. Terminal 5!) in this case is connected directly to theelectrode common to plates 42 and 43 and to the outer electrode of plate45 while terminal 5| is connected directly to the outer electrode ofplate 42 and to the electrode common to plates 44 and 45.

In view of the description of the operation of the Figure 5 embodimentof the invention which has been given above, it is deemed entirelyunnecessary to give a detailed description of the operation in Figure 6.It is sumcient to 'saythat the arrangement is such that, uponapplication of an alternating voltage to terminals 50, 5|, correspondingbending movements of the operating element including plates 42 to 45 areprovided.

Conversely, a vibratory bending movement of the operating elementcomprising plates 42 to 45 results in the generation of an alternatingvoltage which is available at terminals 50, 5|. The arrangement ofFigure 5 or the arrangement of Figure 6 may be used, for example, in apickup device similar to that of Figure l.

i The arrangement of Figure 'l is generally similar to that of Figure 2and corresponding elements have identical reference numerals whilesimilar elements have identical reference numerals primed. The circuitarrangement of Figure 7 is identical to that of Figure 2 and the onlydifference in the arrangement is that the layers of actuating materialhaving electrodes I5, l1, l8 are of circular shape in the of Figure '7.From the description which has been given in connection with Figure 2and in connection with Figure 1 of the above-mentioned arrangementcopending application, it will be seen that the arrangement of Figure 7is such that in its operation one of the plates expands in all radialdirections while the other plate contracts in all radial directions, andvice versa. Thus the arrangemet of Figure '7 effectively provides anactuating element of the diaphragm type wherein, upon application of thepolarizing potential 32, an alternating voltage at the input circuit oftube is associated with cup shaped bending motions of the operatingelement.

Each of the embodiments, of the invention, as

will readily be understood by those skilled in the art, can be usedeither as a generator of a1temating voltages in response to bendingmotions of the actuating element or can be used to provide mechanicalvibratory motion in response to an alternating current input thereto.

While the invention has been described with a certain degree ofparticularity, it is to be under stood that it has been by way ofexample and that changes can be made without departing from the spiritand scope of the invention.

I claim as my invention:

1. A bender-type electromechanical device comprising, an even number ofsuperimposed layers of dielectric material comprising two groups ofelements one group of which is to expand and the other group of which isto contract and vice versa to provide a bender-type of electromechanicaltransducer element, unidirectional electrical-polarizing means for eachof said layers, and electrical terminal-circuit connections to each ofsaid layers such that the charges associated with a theoreticalapplication of voltage thereto are of the same sign in each of saidlayers of one of said two groups of elements as the charge in each suchlayer due to said polarizing means while the charges in each of saidlayers of the other of said two groups of elements due to said appliedvoltage are of opposite sign from the charge in each such layer due tosaid such polarizing means whereby said device can be used to convertbending movements of said such transducer element into electrical energyor vice versa.

2. A bender-type electromechanical device comprising, two layers ofdielectric material effectively comprising two groups of elements onegroup of which is to expand while the other group is to contract andvice versa to provide a bender-type of electromechanical transducerelement, unidirectional polarizing means for each of said layers, andelectrical terminal-circuit connections to each of said layers such thatthe charge associated with a theoretical application of voltage theretois of the same sign in one of said layers as the charge due to saidpolarizing means while the charge in the other of said layers due tosaid applied voltage is of opposite sign from the charge due to saidpolarizing means, whereby said device can be used to convert bendingmovements of said transducer element into electrical energy or viceversa.

3. A bender-type electromechanical device comprising an even number ofrelatively thin and elongated layers of dielectric material comprisingtwo groups of elements one group of which is to expand while the othergroup is to contract and vice versa to provide a bender-type ofelectromechanical transducer element, unidirectionalelectrical-polarizing means for each of said layers, and electricalterminal circuit-connections to each of said layers such that thecharges associated with a theoretical application of voltage thereto areof the same sign in each 01 said layers of one of said two groups ofelements as the charge in each such layer due to said polarizing meanswhile the charges in each of said layers of the other of said two groupsof elements due to said applied voltage are of opposite sign from thecharge in each such layer due to said such polarizing means, wherebysaid device can be used to convert bending movements or said suchtransducer element into electrical energy or vice versa.

4. A bender-type electromechanical device comprising an even number ofrelatively thin circular disks of dielectric material comprising twogroups of elements one group of which is to expand radially while theother group is to contract radially and vice versa to provide abendertype of electromechanical transducer element, unidirectionalelectrical-polarizing means for each of said disks, and electricalterminal-circuit connections to each of said disks such that the chargesassociated with a theoreticaI application of voltage thereto are of thesame sign in each of said disks Of one of said two groups or elements asthe charge in each such disk due to said polarizing means while thecharges in each of said disks of the other of said two groups ofelements due to said applied voltage are of opposite sign from thecharge in each of said disks due to such polarizing means, whereby saiddevice can be used to convert cup-like bending movements of saidtransducer element into electrical energy or vice versa.

5. A bender-type electromechanical device comprising, an even number ofsuperimposed layers of dielectric material comprising two groups ofelements one group or which is to expand while the other group is tocontract and vice versa to provide a bender-type of electromechanicaltransducer element, unidirectional electrical-polarizing means for eachof said layers, electrical terminal-circuit connections to each of saidlayers such that the charges associated with a theoretical applicationof voltage thereto are of the same sign in each of said layers of one ofsaid two groups of said elements as the charge in each said layer due tosaid polarizing means while the charges in each of said layers in theother of said two groups of elements due to said applied voltage are ofopposite sign from the charge in each such layer due to said polarizingmeans, means for mechanically vibrating said transducer element, andelectrical output means coupled to said terminal circuit connections forderiving and utilizing a corresponding electrical output from saidtransducer element.

6. A bender-type electromechanical device comprising, an even number ofsuperimposed layers of dielectric material comprising two groups ofelements one group of which is to expand while the other group is tocontract and vice versa to provide a bender-type of electromechanicaltransducer element, unidirectional electrical-polarizing means for eachof said layers, electrical terminal-circuit connections to each of saidlayers such that the charges associated with a theo retical applicationof voltage thereto are of the same sign in each or said layers of one ofsaid two groups of said elements as the charge in each,

said layer due to said polarizing means while the charges in each ofsaid layers in the other 01 said two groups of elements due to saidapplied voltage are of opposite sign from the charge in each such layerdue to said polarizing means, means for supplying alternating electricalenergy to said electrical terminal-circuit connections, and means forderiving and utilizing a corre- 10 spending mechanical vibration fromsaid traps- OTHER REFERENCES ducer element.

HANS JAFFE. E. W-ainer, Trans Electra Chemical Society, vol.

7 89, pgs. 331-356, 1946. REFERENCES CITED W. G. Cady, Piezoelectrlcity,pgs. 4, 198, 233- 235, 260, 261, 614, McGraw Hill, 1946.-

B. M. Wul 8: I. M. Goldman, C. R. Acad. Sci. URSS, vol. 46, pgs. 139,154 (1945), vol. 49, pgs.

The following references are of record in the file of this patent:

UNITED STATES PATENTS 177-180, Library of Congress.

Nam m v 10 A. DeBretteville, Jr., Phys. Rev. 69; 687 (1946). 33 52 5Mommiunnufi Jan. x P. R. Coursey and K. G. Brand, Nature. 157; 2,402,515Wainer June 18. 1946 297%98 (1946)- 2,424,111 Navlas July 15, 1947

